Could the magnitude 6.5 Greece earthquake trigger another large shock?

Not only have there been many large shocks in this region during the past century (eight M≥6.5 events within 80 km, a rate of one a decade), but they often strike in pairs. M=6.5 and M=6.8 events stuck one day apart in 1953, and M=6.4 and M=6.5 events struck two months apart in 1948 on either side of the epicenter of the 2015 shock. Thus, the possibility that the 17 November shock could be part of a twin cannot be discounted.

17 Nov M=6.5 Nidri Greece earthquake trigger

The 17 November 2015 Mw=6.5 Nidri Greece earthquake struck in a highly active region in northwest Greece, at the junction of three active faults. Broadly, the ‘Nubia’ tectonic plate is impinging on Greece from the east at a rate of 6 millimeters per year, shoving the crust of the Ionian Sea beneath mainland Greece.

Large earthquakes often start or strike at the intersection of faults, as appears occurred here. The plate boundary is fractured into several active faults, including the Kephallonia fault to the south of the epicenter, which slips in a right-lateral sense at a rate of 5-20 mm/yr. (‘Right-lateral’ means that whatever side of the fault you are on, the other side slides to the right). For comparison, the San Andreas (California), and North Anatolia (Turkey) faults slip at about 25 mm/yr. Extending north of the epicenter is the right-lateral Lefkada fault, slipping at 4-8 mm/yr in a right-lateral sense. Intersecting the epicenter from the northwest is the Kerkya thrust fault, slipping 1-2 mm/yr. The mechanism of this quake suggests that the fault ruptured the Kephallonia-Lefkada system, with some thrust motion as well.

[Data from USGS, SHARE, and the ISC-GEM seismic catalog; map base from Google Earth. Interpretation by Ross S. Stein, Temblor, Inc. Nov 17, 2015]

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  • Andreas Karakonstantis

    Does this conclusion comes up by a performed Coulomb Stress Transfer analysis from the available data or is it a statistical approach with the available seismic history?If we hypothesize that a second one, at about the same magnitude, comes up which segment is suggested that will be ruptured?Do these conclusions come from a paper that is in the course to be published?

    • Ross S. Stein

      We used the SHARE (Seismic Hazard Harmonization of Europe) active fault database maintained by ETH Zurich, and the ISC-GEM seismic catalog to draw preliminary conclusions based on past earthquake behavior and the faults in this region. To perform a realistic Coulomb stress transfer calculation, we would need a ‘finite source model,’ which tells us which part of which fault ruptured, and by how much. As far as we know, this is not yet available. — Ross S. Stein